1. Field of the Invention
The present invention relates to a method and an apparatus for recovering a line spectrum pair (LSP) parameter for speech decoding, and more particularly, to a method and an apparatus for recovering an LSP parameter when frame loss occurs and a speech decoding apparatus using the same.
2. Description of the Related Art
To transmit data in a limited bandwidth environment, a speech coding apparatus does not transmit an actual speech signal but extracts parameters representing the speech signal, encodes the extracted parameters, and generates a speech packet including the coded parameters. A speech decoding apparatus decodes the coded parameters included in the generated speech packet and recovers the speech signal using the decoded parameters.
A line spectrum pair (LSP) parameter is one parameter representing the speech signal. The LSP parameter has good coding characteristics since it is closely related to a speech frequency. Most speech coding apparatuses generate the LSP parameter, code the generated LSP parameter, and speech decoding apparatuses decode the coded LSP parameter.
However, to remove an error from a received speech packet, speech coding apparatuses usually check the received speech packet and, if it is determined that the received speech packet has an error, erase the speech packet. Such erasure of a speech packet causes loss of the LSP parameter and breaking of the recovered speech signal.
To solve such problems, a method of recovering the lost LSP parameter in speech decoding has been proposed.
FIG. 1 illustrates a conventional method of recovering an LSP parameter based on the International Telecommunication Union (ITU) G.729 standard. The conventional method illustrated in FIG. 1 is an extrapolation method in which the LSP parameter LSP(m) (or an LSP vector) of a previous good frame (PGF) is not corrected but the LSP parameter LSP(m) is used for L subsequent erased frames.
However, since the same speech signal is recovered for the L frames, continuity between a speech signal recovered for the L subsequent erased frames and a speech signal recovered based on a next good frame (NGF) deteriorates.
FIG. 2 illustrates another conventional method of recovering LSP parameters. The method illustrated in FIG. 2 is an interpolation method in which the LSP parameter of the PGF and the LSP parameter of a next good frame (NGF) received is used after erasing L subsequent frames is used.
The letter w denotes a weight and is determined as a value from 0 to 1 according to the number of the erased frames and whether transmission position of erased frames approaches the PGF or the NGF. Accordingly, the LSP parameter of the L erased frames generated using the LSP parameters of the PGF and the NGF have different values LSP(m+1) . . . LSP(m+x) . . . LSP (m+L).
However, since the LSP parameters are recovered in an LSP parameter region, it is difficult to define a spectrum region, develop an algorithm, and apply the method to a variety of technologies.